Fluorinated ion exchange polymers having carboxylic acid and/or sulfonic acid functional groups or salts thereof are known in the art. One principal use of such polymers is as a component of a membrane used to separate the anode and cathode compartments of a chloralkali electrolysis cell. Such membrane can be in the form of a reinforced or unreinforced film or laminar structure.
It is desirable for use in a chloralkali cell that a membrane provide for operation at low voltage and high current efficiency, and thereby at low power consumption, so as to provide products of high purity at low cost, especially in view of today's high cost of energy. Membrane strengthened by having reinforcement therein is often required by large segments of the chloralkali industry, so as to resist damage during installation and use in cells of industrial size.
Previously known reinforced membranes for chloralkali use, having both carboxylate and sulfonate fluorinated polymer layers, reinforced with fluorocarbon polymer strands and having channels within the membrane left by removal of sacrificial threads embedded therein, provided chloralkali cell performance at acceptably good current efficiency, about 96%. However, these membranes operate at voltages now considered too high, i.e., about 3.5 volts in narrow gap cells and about 3.7 volts in zero gap cells at 3KA/m.sup.2 and 90.degree. C. In an effort to improve the performance of such reinforced membrane, it has been proposed to use a gas release layer, such as a coating containing zirconium oxide or a thin sheet of asbestos paper, which is applied to the carboxylate surface (the surface facing the cathode) of the membrane. However, while this has helped to improve the voltage to about 3.3 volts in narrow gap cells and about 3.2 volts in zero gap cells, the current efficiency has been unexpectedly and unacceptably lowered to about 88-89% in both types of cell, the net result being a power consumption about the same as that before the gas release surface was applied to the carboxylate surface of the membrane.
Inasmuch as the chloralkali industry is moving toward use of zero gap and narrow gap cells so as to minimize the contribution of electrolyte resistance on total cell voltage, it is important to provide for use in such cells reinforced membrane which is adapted to operate at both low voltage and high current efficiency.
It is a principal object of this invention to provide reinforced cation exchange membrane which is especially adapted for zero-gap and narrow-gap chloralkali cells to provide for operation at high current efficiency and low voltage. Other objects will be apparent hereinbelow.